SDF Files

The SDI hardware converts the serial data and clock to 32-bit parallel words and stores them in an 256K by 32-bit FIFO. When 128K words have been collected, the ingestor software transfers 128K words to an SDF file in the ingestor's hard drive. Eight transfers are required to build a 1,048,576 byte (1 MB) SDF file. Thus, each SDF contains 8,388,608 satellite data bits.

Data Storage Requirements

To determine the number of seconds per SDF, divide 8,388,608 by the satellite's bit rate. For example, GVAR's data rate is 2,111,360 bits per second. Therefore, each SDF provides 3.973 seconds of data storage (8,388,608/2,111,360=3.973). At this rate, 906 SDFs are generated per hour.

The data in each SDF file includes all data types sent. Nothing is stripped out and there are no byte aligned boundaries. Thus, new data blocks can start anywhere in any SDF word.